The present invention relates to tire inflation pressure regulators, and more particularly to such regulators that can be installed or mounted directly on a conventional tire valve stem.
A great deal of government and industry attention has been focused on the problems associated with under-inflated vehicle tires. Tires naturally lose air pressure because of permeation through the tire wall at the rate of about two pounds per square inch (PSI) per month. Under-inflated tires adversely affect vehicle handling, can lower hydroplaning speed, and increase stopping distance. Under-inflation also increases the rolling resistance of tires, leading to reduced fuel economy, increased hydrocarbon and toxic chemical emissions, and reduced tire life due to an increase in tire wall temperature and increased tread wear.
On a national scale, these problems have a significant impact on safety, energy usage, the environment, and waste management. For example, the National Highway Traffic Safety Administration (NHTSA) estimates that 533 fatalities per year are attributable to tire defects. Most defects are related to under-inflation.
Studies have found that fuel efficiency is reduced by one percent for every three PSI of under-inflation. A 2001 NHTSA study found that forty percent of automobiles had at least one tire under-inflated by at least six PSI. The Environmental Protection Agency (EPA) has estimated that as much as six billion gallons of gasoline (12.6 billion gallons of crude oil) could be saved annually by a fuel efficiency increase of just one mile per gallon (mpg). Proper tire inflation would make a substantial contribution toward achieving this increase in fuel efficiency. Fuel inefficiency also adds to the world's growing carbon dioxide emissions problem. Each gallon of gasoline used releases 20 pounds of carbon dioxide into the atmosphere.
In the U.S., more than 280 million tires are scrapped every year. Because it requires 1.75 gallons of fuel to produce one tire, millions of gallons of fuel could be saved annually by reducing tire wear and extending tire life through proper inflation.
Congress addressed these problems in 2000 by passing the Transportation Recall Enhancement, Accountability and Documentation (TREAD) Act, which mandates vehicle manufacturers to phase in tire pressure monitoring systems (TPMS) on all new light vehicles (i.e. those under 10,000 pounds). Sep. 1, 2007 was the date for full compliance. A TPMS informs the driver by means of a dash-mounted warning light when one or more of the tires is under-inflated. Because of cost and technology limitations, some TPMS may only alert the driver when pressure drops 25 percent or more below the manufacturer's recommended pressure. This could be over eight PSI, which many in the tire industry feel is an inadequate safety margin. Other problems with TPMS include failure of the driver to respond to the warning light. For example, it is possible that drivers may see the light come on when the tires are cold, but turn off after driving for a while which warms the tires and thereby raises the tire pressure. Drivers therefore may believe that the problem is not significant and that they can wait to service their tires. Or they may believe that the TPMS is faulty, in which case they may simply ignore it. Some TPMS even have a switch that allows a driver to turn off the warning light.
While the benefits of maintaining proper tire pressure are well documented, drivers do not always take action in response to the warning light because inflating tires is an unpleasant, dirty, inconvenient, and time-consuming task. Often the equipment needed to accurately inflate tires is not available when needed. Accurate inflation requires a pressure gauge as well as an adequate source of compressed air. Further, inflation should be performed when the tire is cold or the vehicle has been stationary for at least three hours. Without a pressure gauge, there is no way to reliably set pressure to the manufacturer's recommended level. If the tire is warm, then it is difficult for the driver to determine how much air to add so that there will be adequate pressure when the tire is cold. Vehicle manufacturers specify the cold tire pressure to assure there is adequate load carrying capability in the tire at the coldest service temperature.
As an alternative or supplement to TPMS, onboard automatic inflation systems have been available for many years for trucks and recreational vehicles. These systems include air compressors, individual tire pressure sensors, and the necessary valves and controls needed to automatically maintain proper pressure in each tire. Although these systems are potentially available for automobile use, their relatively high cost and complexity have inhibited their widespread use by light vehicle manufacturers.